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Mineralogical Study of Sediment Samples of Kachua, Chandpur District for Investigation of Arsenic Bearing Minerals

NASIR AHMED
Isotope Hydrology Division, Institute of Nuclear Science & Technology, Atomic Energy Research Establishment, Ganakbari, Savar, Dhaka, Bangladesh

MOHAMMAD MIKAIL
Isotope Hydrology Division, Institute of Nuclear Science & Technology, Atomic Energy Research Establishment, Ganakbari, Savar, Dhaka, Bangladesh

D. K. SAHA
Materials Science Division, Atomic Energy Centre, Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Sixteen sediment samples of different depth (up to 122 m) were studied by X-ray diffraction (XRD) method. The samples were collected from a test borehole, which was drilled by Bangladesh Water Development Board (BWDB) at Kachua, Chandpur district. All the samples were characterized and different minerals have been identified in the samples. Quartz is the major mineral and was found to be in the range of 54.97 - 97.88 %. Two arsenic bearing minerals namely, iron arsenate, Fe₂As(AsO4)3 and arsenic selenide telluride, AsSe0.5Te2 were found in the samples of depth 55.20 m and 100.60 m, respectively. Bangladesh Atomic Energy Commission (BAEC) in collaboration with the United States Geological Survey (USGS) conducted the groundwater sampling campaign for shallow and deep tubewells in Kachua upazila. From the hydro-chemical results, the concentrations of arsenic in shallow tubewells were found above the maximum permissible limit (50 ppb). Concomitantly, the mineralogical study of sediment samples in the same area reflects that the shallow aquifers of Kachua upazila are contaminated by arsenic due to the presence of arsenic bearing minerals.

Keywords: Sediment samples, Kachua, Arsenic bearing minerals

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land development productivity

Objectives:

In the present study XRD method was used to identify the arsenic bearing minerals in underground sediment of arsenic affected area of Kachua upazila under Chandpur district.

Methodology:

DESCRIPTION AREA Kachua upazila under the Chandpur district is considered as highly arsenic affected area. Almost all the shallow hand tubewells water are highly arsenic contaminated. The test hole drilling site was selected at village Srirampur, Union-Karaia. Kachua Upazila. SAMPLE COLLECTION AND PREPARATION: A test hole was drilled by Groundwater Hydrology, Bangladesh Water Development Board (BWDB) down to 326 m to assess the sediment lithology, formation thickness and aquifer properties in the study area. EDECO strata Drill Rig was used to collect the sediment samples applying the direct hydraulic rotary method. A heavy duty mud pump, FJ casings of 152 mm dia, 76 mm dia NW drilling rod, 140 mm dia carbide and roller bits, split spoon and Denison samplers of 76 mm dia etc. were used during drilling process. A number of sediment samples were collected in PVC liner. A few samples were also collected in polythene bags, which were of wash boring. For mineralogical study purposes, the sediment samples were collected at different depth down to 122 m. At first the collected samples were dried in an oven by fixing the temperature 65°C. After the samples become moisture free, about 5g sample was grinded to fine powder in an agate mortar and pestle to get an average particle size < 50 µm. An aluminum sample holder with a central groove of 15 × 10 × 1 mm3 dimension was used as a sample holder and the fine powdered sample ( ≈1g) placed into the groove. The surface of the sample was made sufficiently smooth using glass slide. AQUIFER SYSTEM IN THE STUDY AREA: A lithological cross-section is drawn based on borelogs of BWDB and GSB. 2 to observe the formation thickness as well as aquifer system in the area. The aquifer system at the study site can be divided into three fairly distinct systems. The upper aquifer system or 1st aquifer is essentially the shallow aquifer, the middle or 2nd aquifer system has generally been called the deep aquifer and the deeper system or the 3rd aquifer is newly discovered at this site. EXPERIMENTAL SYSTEM A Philips X’Pert PRO X-ray diffractrometer was used to get X-ray data for the samples at the Materials Science Division, Atomic Energy Centre, Dhaka, with a primary beam power of 40 kV and 30 mA for Cu radiation. A nickel filter was placed before the P-3 Deeper or 3rd Aquifer Deep or 2nd Aquifer Upper or 1st Aquifer P-3 Deeper or 3rd Aquifer Deep or 2nd Aquifer Upper or 1st Aquifer sample to reduce CuKβ radiation and finally CuKα radiation was only used as the primary beam. A θ-2θ scan was taken from 10 to 100° to get possible fundamental peaks of the minerals present in the sample with the sampling pitch of 0.02° and time for each step data collection was 0.6 sec. Three different samples of each depth were irradiated to get sufficient data. The XRD machine was totally computer controlled and all the data were stored in the hard disk memory of the computer for further analysis.

Source of Information: Journal of Bangladesh Academy of Sciences, Vol. 32, No. 1, 1-12, 2008

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The clay mineral fraction (found in depth 3.2, 49.0, 60.0 and 82.0 m) is dominated by quartz and albite with minor illite and clinochlore. The sediment as a whole is dominated by quartz and albite. From the mineralogical study by XRD method of the sediment samples of Srirampur, Kachua, it is observed that the arsenic bearing minerals are found to be exist in the shallow and deep aquifer zone. As surveyed under the joint collaboration work of BAEC and USGS, the high arsenic contents are also identified in the groundwater of shallow tubewells and in a few deep wells in Kachua area.

Knowledge Management: Journal